The present invention relates to a piezoelectric/electrostrictive device comprising a movable portion being operated based on a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of a movable portion by a piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance and is capable of having the movable portion efficiently operated in a large magnitude.
In recent years, in the fields of optics and magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length and position in sub-micron order has been required, and development has been progressed of the displacement element utilizing displacement due to the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance or the like). For example, as shown in FIG. 14, a piezoelectric actuator 21, in which a fixing portion 25, a movable portion 24, and a beam 26 connecting the two are integrally formed by providing a hole 28 on a plate-like body composed of a piezoelectric/electrostrictive material, and an electrode layer 22 is provided on the beam 26, is disclosed (in the official gazette of Japanese Patent Application Laid-Open No. 10-136665). In the actuator 21, when a voltage is applied to an electrode layer 22, the beam 26 expands or contracts in a direction in which the fixing portion 25 is connected with the movable portion 24 by the inverse piezoelectric effect or the electrostrictive effect, thus making it possible to have the movable portion 24 perform an arc-shaped displacement or a rotational displacement in the plane of the plate-like body.
On the other hand, the official gazette of Japanese Patent Application Laid-Open No. 63-64640 discloses a technique with regard to an actuator utilizing a bimorph, wherein an electrode of the bimorph is split, and by selecting the split electrodes to drive the actuator, precise positioning is performed at a high speed, and for example, the specification shows in FIG. 4 thereof a structure which uses two bimorphs opposed to each other.
However, in the above-described actuator 21, as the displacement in an expanding or contracting direction (namely, the in-plane direction of the plate-like body) of a piezoelectric/electrostrictive material is transmitted per se to a movable portion, there is a problem that an operational quantity of the movable portion 24 is small. Further, the actuator 21, having all the members thereof being composed of a piezoelectric/electrostrictive material which is fragile and comparatively heavy, has another problem, in addition to being low in mechanical strength, and inferior in handling, impact resistance and humidity resistance, that the actuator 21 per se is heavy and is operationally likely to be subjected to an influence of harmful vibrations (for example, residual vibrations or noise vibrations when operated at a high speed).
In order to solve the above-described problems in the actuator 21, a proposition has been made that an elastic filling material is filled into a hole 28. However, when the filling material is used, it is apparent that the efficiency of displacement due to the inverse piezoelectric effect or the electrostrictive effect is decreased.
On the other hand, what is shown in FIG. 4 of the specification of the official gazette of Japanese Patent Application Laid-Open No. 63-64640 is that, in bonding an intermediary member 3 with a bimorph, a portion without a divided electrode is bonded with the intermediary member, and at the bonded portion, an effect of the divided electrode is unable to be utilized. In other words, merely a bimorph portion which is not a displacement generating portion is bonded. Further, a bonding form at a portion where a head is bonded with a bimorph is similar in bonding form. As the result, a bending displacement of the bimorph is developed toward the inner space between the intermediary member and the head, and it is a structure where an action for effectively displacing the head per se toward the outer space is unable to be obtained. In addition, the actuator disclosed in the official gazette of Japanese Patent Application Laid-Open No. 63-44640 is so structured that a displacement generating member and a so-called frame member (intermediary member or the like) are separately prepared, and then adhered to be incorporated, and consequently the bonded state of the frame with the bimorph is so structured to be likely to vary with time in accordance with operation of the bimorph, and also to be likely to cause drifting, exfoliation, or the like. Further, a bonded portion of the bimorph with the intermediary member and a bonded portion of the head with the bimorph, namely a structure having an adhesive agent at a supporting portion of a displacement member, is low in rigidity of the supporting portion, and is so structured that an increase in resonant frequency which is required in high speed operation is also difficult to be obtained.
Of a piezoelectric/electrostrictive device capable of solving such problems, although the applicant of the present invention and others have proposed, in the specification of the Japanese Patent Application No. 11-307845 filed on Oct. 28, 1999, a piezoelectric/electrostrictive device capable of obtaining a large displacement quantity as well as maintaining mechanical strength of a joined portion of a thin plate portion with the movable portion above a predetermined level, a device capable of generating still larger displacement and responding at a higher speed is sought after particularly for precise positioning in the magnetic recording field and optical field.
The present invention is made in view of above-described current situation, and an object thereof is to provide a displacement element which is capable of further increasing a displacement quantity of a movable portion while maintaining the mechanical strength at the joined portion of the thin plate portion with the movable portion above a predetermined level, as well as high in resonant frequency and superior in responsibility, and a sensor element capable of detecting vibrations of the movable portion in finer precision.